Problem: If $x \oplus y = 3x-y$ and $x \boxdot y = x-5y$, find $2 \boxdot (2 \oplus 4)$.
First, find $2 \oplus 4$ $ 2 \oplus 4 = (3)(2)-4$ $ \hphantom{2 \oplus 4} = 2$ Now, find $2 \boxdot 2$ $ 2 \boxdot 2 = 2-(5)(2)$ $ \hphantom{2 \boxdot 2} = -8$.